Electronic key musical instrument

ABSTRACT

An electronic instrument wherein manually operated keys are coupled to a magnetic circuit for controlling flux changes therein, and a pick-up coil develops a voltage whose amplitude is proportional to impact strength of striking the key, and whose duration indicates duration of key depressing movement. The pickup voltage charges a capacitor which is discharged through a transistor gating circuit receiving tone frequency signals whereby these signals are attenuated in accordance with the charge state of the capacitor; several variations of this circuit and supplemental circuitry is disclosed for tone control, simulation of particular instruments, percussion, sustain and other effects.

United States Patent 1191 Rosenberg ELECTRONIC KEY MUSICAL INSTRUMENT [76] Inventor: Werner Rosenberg, Bruder Grimm-strasse I0, 6236 Eschbom, Germany [22] Filed: Dec.6, I971 [21] Appl. No.: 204,858

130 1 Foreign Application Priority Data 1 Dec. 16.1970 Germany ....P2061'95813 [52] US. Cl 84/1.13,' 84/124, 84/126 [51] Int. Cl. Gl0h 3/00 [58] Field of Search 84/1.01, 1.13, 1.24,

84/126, DIG. 8, DIG. 7

[56] References Cited UNITED STATES PATENTS 3,313,877 4/1967 Boenning 84/].01 3,507,970 4/1970 Jones 84/1.01 3,509,263 4/1970 Cordry 84/126 X 3,544,695 12/1970 Dijksterhuis 84/].26 X 3,553,337 1/1971 Dijksterhuis 84/].26 X

1451 July 31, 1973 Adachi 84/124 x Hiyama.... 84/126 x Hiyama.... 84/126 x Hiyama.... 8411.26 x

Ohno 84/ 1.26 X

Primary Examiner-Richard B. Wilkinson Assistant Examiner--U. Weldon Attorney-Ralf I-I. Siegemund I ABSTRACT 1 'An electronic instrument wherein manually operated 16 Claims, 7 Drawing Flgures PATENTibJmai-ms v f Y 3,749,806

1N VENTOR BY 7 W ATTORNEY ELECTRONIC KEY MUSICAL INSTRUMENT The present invention relates to an'electronic key-' operated musical instrument in which the volume of each tone is individually determined by the impact strength of (manual) key actuation. In a'piano of conventional construction, an individual tone is produced in that a key when depressed operates a hammer which impacts against one or several strings. The volume or intensity of the sound producing vibrations of the string depends upon the impulse the'hammer receives by the key operation. It should be notedthat-a keyis not simply depressed'manually, but the player actuates it more x or less forcefully, whereby the particular form of key striking determines the quality of the sound and of the tone thus produced. The transmission of key depression upon the hammer includes arather complicated mechanical structure called action, which has been developed and has matured through many decades. The

strength of the impact and, therefore, the volume of the sound is determined by the force exerted by the finger upon depressing a key; but also the path of the key and the time or duration of actuationand depression determine volume and quality of the sound.

Previously build electronic musical instruments, such as electronic organs, oep rate in that atone is triggered by a switch whereby the volume is not in theleast controlled or influenced by the force with which the keyis struck. Various ways have been suggested how to translate the manual switchoperation into volume control; for example, by means of pressure sensing, or

the like. However, these known arrangements do not result in a proportionality relation between sound volume and impulse (momentum). A- better approximation of the natural piano operation is obtained by using twoswitches and by arranging these switches so that one of them monitors the beginning of key development and the other one the end thereofi A'time element, or timing'circuit, is respectively turnedon and off by means of these switches, so that in fact a voltage is generated which is proportional to key depression speed and is, in turn, used for volume control; However, for this arrangement to work, it is necessary that the key always traverses a given displacement path completely (both switches must always be operated) so that very muted and soft tones through brief key operation are not possible. Also, the generationof aparticular tone is still not well possible by means of such an arrangement.

In other words, the tone production is not completely undercontrol of the player of a conventional electronic instrument. It is an object of the present invention to provide for faithful translation between finger action by a player and the resulting tone vquality and volume. Among the objects of the invention is also the intent to provide construction and circuitry to simulate, for example, the piano forte characteristics of'aregular piano in an electronic, key operated instrument, using particular volume control that is proportional to the impulse (momentum) as it is effective on the key.

In accordance with the preferredembodiment of the present invention, a key is constructed for varying the magnetic flux in amagnetic flux path. As the key is depressed, a flux change occurs within a magnetic circuit that includes a permanent magnet, and a voltage is induced in a pick-up coil. This voltage represents the key impulse in that the amplitude of that voltage is proporfading time constant of thedesired tone. The capacitor voltage controls a gating and modulating'circuit which causes an electric sound generator to produce a tone as associated with a particular key and proportional to the amplitude or the control voltage produced by the electromagnetic circuit outlined above.

While the specification concludes with claims particularly pointing out'and distinctly claiming the subject matter whichis regarded as the invention," the objects and fe'atures ofthe invention and'further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawings in which:

FIG. 1 illustrates somewhatschematically and in a side view, a musical key instrument and control signal generator;

FIG. 1a illustrates top view of the signal generator in FIG. 1;

FIG. 2 illustrates a circuit diagram for processing the control'signal as produced bythe key shown in FIG. I, theFIG. 2 showing additionally voltage signals as they are being produced'in the circuit of FIG. 2;

FIG. 3 illustrates acircuit for producing sustain;

FIG. 4 illustrates a circuit for producing-percussion effect; 2

FIG: 5 shows a circuitdiagram for producing, e.g., the note a" with various tone quality control features and piano action simulation;

, drawings, in FIG. 1 thereof is illustrated an inductive pulse source connected'to and operated by a key T pertaining to an electronic musical instrument. The key T is spring biased by means of a" spring F, illustrated somewhat schematically in the right-hand portion of FIG. 1, there being a pivot point A about which the key T turns when depressed. Key actuation and depression by the player is illustrated by the arrow to the left of the key.

- An induction coil Sp is provided in a manner that the coil loops around a magnetic circuit which includes a permanent magnet M and pole shoes P extending transversely from the pole ends of the magnet. .An' armature E is affixed to the key T and is positioned in particular relation to the pole shoes P. Thearmature B may be a piece of magnetic material, e.g., iron. Normally, armature E is displaced from the-pole shoes P and influences very little the magnetizable circuit. However, upon de- P, and that results in a change of flux in themagnetic circuit, the flux being produced by permanent magnetic M. As a consequence of this flux change, a voltage is induced in coil Sp. The flux changes, as'longas armature E and key T are actually being'moved.

- It should be mentioned that in lieu of a piece of an iron-Boone could use. a permanent magnet, or the permanent magnet M could be affixed to key ,T, and its particularly the duration of that voltage is indicative of the duration of key depressing movement, and the amplitude of that voltage has direct relation to the speed of key actuation, both parameters together define the impulse (momentum) as exerted upon the key T by the player.

FIG. 1 illustrates additionally a contact reed affixed with one end to the wire, the other end connects to armature E. That contact reed engages a busbar for contact closing as long as the key is at rest.

Proceeding now to the description of FIG. 2 there is illustrated'a circuit that processes directly the voltage that is induced in coil Sp. The coil Sp is schematically illustrated again in FIG. 2, and the figure shows additional circuit elements as they are connected to the terminals of the coils. Above the coil is depicted to voltage signal excursion U resulting from key depression. Upon return of the key, a voltage of opposite polarity is induced in coil Sp. This voltage reversal occurs usually upon release of the key, as the key then returns to rest position under the influence of spring F. The following elements are connected to the coil Sp:

There is a diode D connected to a capacitor C, and a biasing battery Us completes a first circuit. The coil Sp as shown is to have very low internal resistance, so that the charge period for the capacitor is very low, i.e., inthe order of milliseconds. That means that in fact the charge on the capacitor and the voltage thereacross follows with little delay the voltage as induced in the coil by the manually operated key. As a consequence, the capacitor will in fact be charged to the peak output voltage of coil Sp. The diode D prevents discharge of l two paths. One path is the collector emitter path of a transistor Tr, the other path leads via a resistor R2 through a load resistance Ra.

The resistor R1 is dimensioned so that the discharge period for capacitor C is relatively large, i.e., it is in the order of seconds. This corresponds to the duration of noticeable vibration or oscillation of a piano string. Therefore, the voltage as produced by key depression is transmitted just as the impulse in the case of a regular piano, and without feedback into the key, and that voltage is available for transmission control of the output of a tone generator.

Such a tone generator is connected to the gate of transistor Tr and schematically denoted at G. However, before proceeding further, some additional remarks are in order.

Aside from the numerous possibilities for controlled tone forming and other audio effects that can be produced in a electronic instrument, there are two particular additional advantages over mechanical instruments that result directly from practicing the present invention. First, the force of operating a key can be reduced, i.e., the minimum force need to depress and to move a key at all can be very much lower than in the case of a regular piano. This, of course, was true also for a regular electronic instrument operating with switches, but it should be noted that in the present case there is a direct translation between impulse produced by finger action of the piano player, and the resulting tone production. Therefore, by reducing the minimum force needed to produce any tone at all, the range of tone formation made available to the player is considerably enlarged, increasing possible versatility in playing accordingly. The reduction of this minimum force or mechanical threshold is particularly noticeable for pianissimo playing.

Of course, the circuit illustrated has its own threshold, particularly as given by the high forward impedance of diode D for small voltages. However, it is the purpose of the biasing voltage Us to bias the diode in forward direction, just to the knee of the voltage/current characteristics thereof. This bias can be made adjustable which may be necessary, as full utilization of the capabilities of such a piano requires actually more than usual profficiency. On the other hand, of course, the versatility of playing increases considerably and is particularly noticeable if the player wants to produce just a whisper of a sound.

Before proceeding with the description of FIG. 2 and to other aspects of the invention, the following reference to known procedures should be interjected that lead to the several advantages of the present invention; Two methods are known for controlling sound and audio frequencies in an electronic organ by means of switches. In accordance with one method, a normally disabled oscillator is enabled. In the other method, the oscillator operates on a continuing basis but its output is gated. The latter circuit is used mostly in electronic instruments, whereby the gating may include amplitude control in order to provide particularly for sustain, percussion and other effects. Here, three different circuits have become known.

First, one can use a d-c voltage as gate control, particularly for controlling the base circuit of a transistor or of the emitter circuit of that transistor, and an a-c voltage connected to the base is thereby gated on. This operation resembles a switching operation more than a gain control and provides,-therefore, amplitude dependent distortions of the signal envelope that represents the tone quality and, therefore, distorts theproduced sound.

Another method includes control of a lamp by means of a switch operated d-c voltage, and the lamp illuminates a photo resistance on the like. The resistance of this light sensitive element is used in voltage divider configuration to gate the output of a sound generator oscillator. This particular circuit is quite expensive and does not operate without distortionseFinally, a circuit is known in which a field-effect transistor is used as a variable resistor and in voltage divider configuration. The output of a tone generator is then controlled accordingly. Again, however, it is an expensive circuit.

On the basis of the description of these prior art methods, it is easier to appreciate another object of the present invention, according to which it is suggested, to provide a circuit which particularly permits utilization of integrated circuits; it is an analog circuit for gating and modulation and operates without distortions. Circuits seemingly resembling the one suggested here have been used otherwise as v a-transistorized inverter or modulation circuit. The particular circuit connected to the capacitor C as illustrated, will in fact produce a controlled sound that decays or fades in accordance with an e-function, and even the smallest amplitude of an a-c output signal is still proportional to capacitor voltage (and to the peak amplitude of the output of the output of coil Sp); that relationship being maintained without distortion. The resulting output is an amplitude controlled wave train as derived from source G. i

The elements R1, R2, Tr and R3 in FIG. 2 establish a modulator circuit which in connection with the pulse source as described permits distortion-free analog gating modulation of the rectangular wave signals provided by generator G, by means of the capacitor voltage as it decays. The output of generator G itself is a pulsating one, as depicted next to the terminal that leads to the'base resistor R3 of the transistor. The generator may, for example, be a multivibrator. The output of that voltage source is, therefore, aseries, of rectangular pulses, and they are permanentlyapplied to thebase" of the transistor Tr via the resistor R3.

Pursuant to operation of this circuit the junction between resistor R1 and R2 is periodically short-circuited and opened. The decaying d-c voltage as furnished by the discharging capacitor C is thereby converted into a sequence of fading rectangular pulses. These pulses as depicted in the upper right-hand'comer of FIG. 2' are fed to the load or utilization circuit represented by resistor Ra. The load Ra includes actually a mixing circuit for the tone signals as they are derived from several depressed keys. The mixed sound signal is fed to a loudspeaker. There may be sound modulating, forming and amplifying circuitry interposed in order to produce particular sound volume and in order to produce particular sound effects.

The modulator circuit as described thus far, and as particularly including capacitor and modulator, may be used in another form for tone control. This is illustrated in FIG. 3, showing a circuit for the sustain effect with control through a switch Ts. In the illustrated circuit, a particular sustain key, operating switch Ts, is depressed, and a capacitor Ca is charged via a resistor Rs to reach the voltage of a source U. The modulator includes transistor Trl, resistors R11, R21 and R31, G being again the generator of a train of pulses. Thegating output by this modulator is-essentially unattenuated as long as switch Ts remains down. As the key for switch Ts is released, the voltage across capacitor Ca decays slowly and so does the tone produced.

Proceeding now to the detailed description of FIG. 4, there is shown how the modulator circuit in accordance with the invention is used for control of percussion. Percussion is controlled here manually by operation of a key acting on'a switch Tsl, there being an auxiliary capacitor Cs and resistor Rsl included,in addition to a diode Db, a capacitor Cb, resistors R13, R23, R33 and transistor Tr3 all provided as before, and the voltage source U can also be the same as in FIG. 3, but U may actually be furnished by the voltage Sp as developed in accordance with FIG. 1. The transistor Tr3 with resistances R13, R23 and R33, are connected as in the other circuits;the source of signal G2 may be the same as described above in reference to FIGS. 2 and 3, or a different one.

As the key operating switch Tsl is depressed, the capacitor Cb receives voltage U in pulsating form, via the capacitor Cs. The voltage so applied to capacitor Cb, however, decays and therefore the sound that is permitted to pass through the gating circuit established by the transistor Tr3, etc., decays immediately, although somewhat slowly. As the key Tsl is released, the capacitor Cs is discharged via the resistor Rsl and that, in turn, prepares the circuit for the next depression of the percussion key t'h'at operates switch Tsl. The voltage U may be provided by another key operated voltage source for an amplitude-vibrato or mandolin effect.

In the circuit shown in FIG; 2 and others, aresidual or leakageaw is established at the collector of transistor, having a few millivolts amplitude, even if capacitor C isdischarged. In order to have a sufficiently high signal-to-noise ratio, the d-c voltage as applied to the capacitor must be in the order of a few volts; in other words, the coilSp must produce a large output; Now, if'one wants to use several footpedals, as is done in an electronic organ to'produce a composite effect from depression of a single key, the capacitor operated by that key. actually has to control several foot-pedal operated modulator stages. However, the coil Sp may not necessarily be able to furnish the required power for such multiple load conditions. Accordingly, an amplifier may have to be connected between coil Sp and diode.

A complete circuit with five foot pedal outputs from l6".'to 2' is illustrated in FIG. 5. Again, there is provided as principle input the coil Sp inwhich a voltage is induced as the key for a particular note, e.g., a" is being depressed. The output of the key operated coil Sp controls a transistor stage Tro requiring only a few volts. Voltage up to 50 volts develops acrossa resistor Rc in the collector circuit of transistor Tro, the operating voltage being dimensioned accordingly. Resistor Re is the emitter bias resistor for this amplifier. A biasing voltage Us suppresses the response threshold of the transistor as well asof the diode D1.

The amplified, key-produced output pulse is fed to capacitor C via diode D1' and stored in the capacitor, just as in FIG. 2. Now, a plurality of modulator circuits of the type shown in FIG. 2 is connected to thecapacitor C; each one is provided'for individual foot pedal position, and each one of these modulator circuits provides for aselective discharge path of the capacitor C.

For the moment we shall disregard the circuit branch Rd-D2-Sdn-Rdg-Sdo, which is a separate branch that connects parallely across the capacitor C, and requires switches Sdn and Sdo to be'closed in order to be effective.

A voltage divider or adjustable resistor Rk operates" Each key for the other notes is provided-with a similar circuit, with a corresponding tone association at the bases of the respective transistors in the several modulator stages. I

The'resistors illustrated with hatching, the switch Sdo and the voltage source Us is provided once for all keys.

The connections designated with X are busses, orlead to busses, which connect to the corresponding points-in the circuits for the other keys. Thus, for each foot pedal position there are provided signal busses just as in the case of an electronic organ, wherein each bus,as a foot pedal operated gate, provides collection" of the several tone signals of all depressed keys independently from the other respective busses.

In order to provide for (i.e., to simulate) the usual damping: as found in a piano, each key is connected to a switch Sdn (see FIGS. I and 5). In normal position of the key when not depressed, this switch Sdn is closed, and the capacitor C discharges via the resistor Rd and Rdg to ground. In other words, there is a permanent short circuitry path across capacitor C for this particular tone. As the a key is depressed, switch Snd opens so that capacitor C can charge without this bypass discharge circuit being effective, and the tone decays slowly. All switches Sdn run to bus Ss which can be grounded via resistor Rdg and switch Sdo. This switch Sdo corresponds to and is operated just as the usual pedal for damping and sustain control in a piano.

The situation, therefore, is as follows:

The capacitor C discharges relatively slowly through one or more transistor circuits if at least one of the switches Sdn and Sdo is open, corresponding to an undamped tone production. This occurs either as long as the a" key is and remains depressed, i.e. held down by the player (Sdn open), or as long as the damping foot pedal (or corresponding key) is depressed for opening switch Sdo. After release of the key (in our example, the a key) and without pressing the damping pedal (or key) or after release thereof, both switches Sdn and Sdo are closed, and the capacitor C discharges relatively rapidly so that the tone (a note) decays rapidly also. Resistor Rd is sufficiently large so that upon release of the damping key the tone does not decay too rapidly, as that would sound unnatural. The common resistor Rdg increases the time constant for the rest position of the keys, which results in reverberation effect. A reverberation is actually produced with maximum intensity when this damping switch Sdo is opened. The diode D2 prevents that capacitor C discharges upon release of the damping key and closing of switch Sdn via the busses and into the other sound producing circuit, stimulating the same; that unwanted stimulation could occur in case the switch Sdo is open.

The circuit illustrated in dashed lines in FIG. 5 can be used for providing a permanent tone as is produced frequently in electronic organs. The switch S0 isclosed as longas the a" key is not depressed, and actually short-circuits coil Sp. Switch S0 opens as soon as the a key is actuated, and does not interfere with normal playing. The resistor Rp leads to a bus which can be connected to a source of negative voltage potential via the common'switch Spo. When key-operated switch Spa closes, transistor Tro is rendered conductive and maintains a constant voltage across capacitor C, but only when switch S0 is opened, by pressing the"a key. When the key is not depressed, closed switch S0 establishes such bias on the base of transistor Tro, that it remains non-conductive. If now switch S0 is opened, then a voltage is developed across the internal resis-- tance of coil Sp, which will control transistor Tro, and the note a is being produced as long as the a key is being depressed. After releasing this particular piano key, the sound decays more or less rapidly in dependence upon the total effective resistance Rd 4- Rdg in the capacitor discharge circuit. The switch So by itself takes also care that in the undepressed position of the.

key, any mechanical vibration set up in the piano will not result in the production of a sound. In other words, the switches So in each key circuit make sure that, for example, a passing truck does not play the piano, the coil Sp remains short-circuited.

In order to provide for tone control, usual and known circuits can be employed with relatively little expenditure using, for example, one filter per'registerand foot dal vibrations. Thus, the busses for the individual organ foot pedal positions are separated into groups of tone frequencies and connected to appropriately tuned LS filters so as to eliminate most harmonics, and clean" sinusoidal vibrations will be the result. For example, a "concert piano needs a sinusoidal tone at 8', supported by 16', some 4' and some 2 are necessary also.

The several different instruments that are to be simulated have difierent (natural) amplitude dependent fading time constants. This dependency can be simulated by means of non-linear resistances that are to be connected parallel to the capacitor C. The difference here, however, may not accoustically be warranted.

Versatility of one instrument is not always required. Rectangular sound waves are usually. employed, as the various effects result from selective filtering, In case only sinusoidal sound waves aredesired, a sine wave generator can readily be used, and the amplitude thereof is controlled by'the voltage across capacitor C, which is a decaying d-c voltage. A circuit of that type is now shown with reference to FIG. 6.

I The circuit illustrated in FIG. 6 includes a delay line K including three RC members, and an amplifier V with a single transistor stage and a return path into the delay line. The time constant of the delay lineK determined the frequency and the gain of the amplifierin damped condition; elements C and D are similar to those of FIG. 2 and connect to a coil Sp as described. The circuit is adjusted so that the resulting oscillation is only very little attenuated, once stimulated or trig-' gered by means of a d-c voltage impulse derived from the capacitor C, which is of course a key-generated voltage. The discharge time constant of the capacitor C is thereafter no longer the determining factor for the attenuation, and can be selected shorter accordingly. The tone frequency signal is taken from output terminal A and fed to an amplifier, such as a power amplifier. A resistor Rv controls gain and attenuation, and

can be connected into the circuit directly as illustrated or it is inductively coupled into the circuit, so that the resistor Rv can be shared by all tones.

The invention is not limited to the embodiments described above but all changes and modifications thereof not constituting departures from the spirit and intended to be included.

flux path, a component of that circuit disposed on the key for displacement therewith and producing a corresponding change of the flux in the flux path when moving;

a pick-up coil magnetically coupled to the magnetic circuit and being responsive to changes of the flux in the flux path,a voltage being inducted in the coil upon depressing the key; switch means operated by the key for short circuiting the coil when the key is not depressed and for.

polarity for biasing the diode to the conduction threshold thereof so as to substantially remove the effectiveness of the threshold in the circuit; and

second means including a modulator connected across the capacitor and further including a source for audio frequency signals connected for controlling the modulator for causing the modulator to provide an attenuated tone signal in dependence upon the capacitor dischaiige.

2. In an instrument as in claim 1, the magnetic circuit including a permanent magnet for obtaining production of magnetic flux in the circuit. 7

3. In an instrument as in claim 1, the key provided with an armature movable relative to stationary components of the magnetic circuit.

4. In an instrument as in claim 1, and including a sec,- ond switch on the key, the second switch pertaining to an attenuating circuit when the key is depressed, the second switch enabling the attenuating circuit to provide relative rapid discharge of the capacitor.

5. In an instrument as in claim 4, and including a third switch, corresponding to a sustain pedal of a piano, for disabling the attenuating circuit.

6. In an instrument as in claim 1, the second means including a plurality of modulators, each receiving signals of different frequencies, including the fundamentals of a note.

7. In an instrument as in claim 6, the modulators of the plurality connected respectively to receive tone signals of particular frequency relation to the respective fundamental of the note.

8. In an instrument as in claim 1, including fourth switching means for applying a voltage to the capacitor as long as the key remains depressed, independently from the development of voltage across the coil, further including fifth switching means overriding the operation of the fourth switching means.

9. In an instrument as in claim I, the second means including a sine wave generator, connected for being triggered upon charging the capacitor by the voltage across the coil, the sine wave generator including a delay line and an amplifier forming a closed loop.

10. In an instrument as in claim I, and including an amplifier between the said coil-switch means arrange,-

ment and the said capacitor-diode circuit, said biasing source compensating also the amplifier'threshold.

11. In a key operated electronic instrument, the improvement comprising: first means including a key for providing a dc-voltage corresponding to the velocity with which the key is depressed a diode capacitor series circuit connected to said first means for charging the capacitor in dependence upon the said dc-voltage; and a transistor circuit including a transistor having main electrodes and a control electrode and being connected with its main electrodes across the capacitor for controlling the discharge of the capacitor when conductive, the transistor circuit further having the control electrode of the transistor connected to a tone frequency signals, said source causing alternating between high and low impedance in the transistor as effective across the capacitor for discharge thereof so that the capacitor voltage controls increasing attenuation of the tone frequency signals as derivable from the circuit. 12. In an instrument as in claim 11, including a series circuit of a resistor of a diode, of a first switch and of a second switch, for providing a discharge by-pass for the capacitor when the first and secondswitches are both closed, so that the tone attenuation in the transistor circuit is enhenced, the first switch disposed to open when and as long as the key is depressed, the second switch opening in response to operation corresponding to sustain pedal operation of a piano.

13. In a key operated instrument as in claim 4, there being a plurality'of transistor circuits connected across the capacitor, each transistor circuit receiving and attenuating a different tone frequency signal corresponding to the capacitor voltage as discharging.

14. In a key operated instrument as in claim 11, including a transistor amplifier connected between the first means and the diode-capacitor-circuit, further including biasing means in the transistor amplifier circuit for causing the key to trigger charging of the capacitor and maintaining charge on the capacitor as long as the key is depressed.

15. In a key operated instrument as in claim 11, the first means including a pick-up coil on a magnetic circuit, the magnetic circuit including a displaceable member disposed on the key for flux control of the circuit, a voltage being induced in the coil when the key is being depressed.

16. In a key operated instrument as in claim 16, including an amplifier connected to the coil to supply voltage to the capacitor, and switching means for varying bias on the amplifier for controlling the signal transmission charaeteristic between coil and capacitor.

. i I t It I 

1. In a key operated electronic instrument, in which the intensity of striking a key is to be translated into a tone having amplitude or volume proportional to the impulse momentum of key actuation, the improvement comprising: a manually depressible key; first means for defining a magnetic circuit and closed flux path, a component of that circuit disposed on the key for displacement therewith and producing a corresponding change of the flux in the flux path when moving; a pick-up coil magnetically coupled to the magnetic circuit and being responsive to changes of the flux in the flux path, a voltage being inducted in the coil upon depressing the key; switch means operated by the key for short circuiting the coil when the key is not depressed and for opening the short circuit when the key is depressed; a series capacitor-diode circuit connected to the coil for charging the capacitor when the coil develops a voltage of one polarity upon depressing the key, the diode preventing discharge of the capacitor when the voltage reverses; a dcbiasing source connected in series with said diode and said coil, at a polarity for biasing the diode to the conduction threshold thereof so as to substantially remove the effectiveness of the threshold in the circuit; and second means including a modulator connected across the capacitor and further including a source for audio frequency signals connected for controlling the modulator for causing the modulator to provide an attenuated tone signal in dependence upon the capacitor discharge.
 2. In an instrument as in claim 1, the magnetic circuit including a permanent magnet for obtaining production of magnetic flux in the circuit.
 3. In an instrument as in claim 1, the key provided with an armature movable relative to stationary components of the magnetic circuit.
 4. In an instrument as in claim 1, and iNcluding a second switch on the key, the second switch pertaining to an attenuating circuit when the key is depressed, the second switch enabling the attenuating circuit to provide relative rapid discharge of the capacitor.
 5. In an instrument as in claim 4, and including a third switch, corresponding to a sustain pedal of a piano, for disabling the attenuating circuit.
 6. In an instrument as in claim 1, the second means including a plurality of modulators, each receiving signals of different frequencies, including the fundamentals of a note.
 7. In an instrument as in claim 6, the modulators of the plurality connected respectively to receive tone signals of particular frequency relation to the respective fundamental of the note.
 8. In an instrument as in claim 1, including fourth switching means for applying a voltage to the capacitor as long as the key remains depressed, independently from the development of voltage across the coil, further including fifth switching means overriding the operation of the fourth switching means.
 9. In an instrument as in claim 1, the second means including a sine wave generator, connected for being triggered upon charging the capacitor by the voltage across the coil, the sine wave generator including a delay line and an amplifier forming a closed loop.
 10. In an instrument as in claim 1, and including an amplifier between the said coil-switch means arrangement and the said capacitor-diode circuit, said biasing source compensating also the amplifier threshold.
 11. In a key operated electronic instrument, the improvement comprising: first means including a key for providing a dc-voltage corresponding to the velocity with which the key is depressed a diode capacitor series circuit connected to said first means for charging the capacitor in dependence upon the said dc-voltage; and a transistor circuit including a transistor having main electrodes and a control electrode and being connected with its main electrodes across the capacitor for controlling the discharge of the capacitor when conductive, the transistor circuit further having the control electrode of the transistor connected to a tone frequency signals, said source causing alternating between high and low impedance in the transistor as effective across the capacitor for discharge thereof so that the capacitor voltage controls increasing attenuation of the tone frequency signals as derivable from the circuit.
 12. In an instrument as in claim 11, including a series circuit of a resistor of a diode, of a first switch and of a second switch, for providing a discharge by-pass for the capacitor when the first and second switches are both closed, so that the tone attenuation in the transistor circuit is enhenced, the first switch disposed to open when and as long as the key is depressed, the second switch opening in response to operation corresponding to sustain pedal operation of a piano.
 13. In a key operated instrument as in claim 4, there being a plurality of transistor circuits connected across the capacitor, each transistor circuit receiving and attenuating a different tone frequency signal corresponding to the capacitor voltage as discharging.
 14. In a key operated instrument as in claim 11, including a transistor amplifier connected between the first means and the diode-capacitor circuit, further including biasing means in the transistor amplifier circuit for causing the key to trigger charging of the capacitor and maintaining charge on the capacitor as long as the key is depressed.
 15. In a key operated instrument as in claim 11, the first means including a pick-up coil on a magnetic circuit, the magnetic circuit including a displaceable member disposed on the key for flux control of the circuit, a voltage being induced in the coil when the key is being depressed.
 16. In a key operated instrument as in claim 16, including an amplifier connected to the coil to supply voltage to the capacitor, and switching means for varying bias On the amplifier for controlling the signal transmission characteristic between coil and capacitor. 